spaceSpace and Physics

Serendipitous Observations Spot Stars Too Dim To See


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockFeb 3 2020, 15:49 UTC

Artist's impression of the microlensing stellar pair. M. R?bisz/ESA

The European Space Agency’s Gaia mission is conducting some incredible observations of the Milky Way, providing new insights into the many stars we can see in the sky. And, it turns out, it can also tell us more about the stars that we can’t see.

As reported in Astronomy & Astrophysics, Gaia spotted a distant star around 49,000 light-years away suddenly brightening and dimming. Then, after a few weeks, it brightened and dimmed again. The event, known as Gaia16aye, was utterly peculiar. The dimming happened within one day, something no other supernova or star has been known to do.


It turns out that the star wasn’t doing anything. The change in brightness was due to two other stars located much closer to Earth, roughly 2,500 light-years away. These are too dim to be visible but their gravity, thanks to their alignment in the sky, acted as a lens, changing the brightness of the more distant object.

Microlensing, as this phenomenon is known, is often used in astronomy to study the invisible, such as dark matter or black holes. This is the second microlensing event detected by Gaia, but it really mystified the researchers as it didn’t look at all like the previous event.

“If you have a single lens, caused by a single object, there would be just a small, steady rise in brightness and then there would be a smooth decline as the lens passes in front of the distant source and then moves away,” lead author Łukasz Wyrzykowski, from the Astronomical Observatory at the University of Warsaw, Poland, said in a statement.


“In this case, not only did the star brightness drop sharply rather than smoothly, but after a couple of weeks it brightened up again, which is very unusual. Over the 500 days of observation, we have seen it brighten up and decline five times.”

The best explanation for the peculiarities is that it was not just one star microlensing, but two. The team collected enough information to be able to tell that the two stars are red dwarfs 0.57 and 0.36 times the mass of our Sun, respectively. Their distance is about twice the distance between the Earth and the Sun and they orbit the common center of mass in 2.88 years.

“We don’t see this binary system at all, but from only seeing the effects that it created by acting as a lens on a background star, we were able to tell everything about it,” added co-author Przemek Mróz, a postdoctoral scholar at the California Institute of Technology.


The study was possible thanks to follow-up observations from 50 different observatories worldwide, allowing for continuous monitoring of this special event.  

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